Composition and method for color passivation of zinc and cadmium

ABSTRACT

A composition comprising a mixture of hexavalent chromium compounds such as chromic anhydride and soluble chromates, and soluble nitrates, soluble sulphates, soluble boron compounds, and an amino acid, said composition having the following content of the above components (in weight parts): HEXAVALENT CHROMIUM COMPOUND(CALCULATED AS CHROMIUM)1.7-70.0 NITRATE COMPOUND (CALCULATED AS NO3 )1.0-45.0sulphate compound (calculated as SO42 )1.0-25.0boron compound (calculated as boron)0.5-10.0amino acid0.5-6.0 Passivation is effected by dipping the workpieces into an aqueous solution of said composition for a period of 3 to 90 seconds at a temperature of 15* to 35*C.

United States Patent [191 Sharmaitis et al.

[ 1 Dec. 17, 1974 1 COMPOSITION AND METHOD FOR COLOR PASSIVATION OF ZINC AND CADMIUM [22] Filed: Dec. 29, 1972 [21] Appl. No.: 319,391

[30] Foreign Application Priority Data Apr. 5, 1972 U.S.S.R 1762901 [52] U.S. Cl. 148/621, 148/62 [51] Int. Cl. C23f 7/26 [58] Field of Search 148/621, 6.2

[56] References Cited UNlTED STATES PATENTS 2,904,414 9/1959 Ostrander et a1. 148/621 3,121,032 2/1964 Seyb 148/621 2,483,510 10/1949 Stareck 148/621 3/1967 Freeman 148/6.21 7/1970 Holden et al. 148/62 Primary 'Examiner-Ralph S. Kendall Attorney, Agent, or FirmHolman & Stern [57] ABSTRACT A composition comprising a mixture of hexavalent chromium compounds such as chromic anhydride and soluble chromates, and soluble nitrates, soluble sulphates, soluble boron compounds, and an amino acid, said composition having the following content of the above components (in weight parts):

hexavalent chromium compound (calculated as chromium) 1.7-70.0 nitrate compound (calculated as N00) 1.045.0 sulphate compound (calculated as SO 1. 25.0 boron compound (calculated as boron) 0.5l0.0 amino acid 0.5-6.0

12 Claims, No Drawings The present invention relates to improvements in compositions and methods for the chemical treatment of metal surfaces, and more particularly to a composition and a method for color passivation of zinc and cadmium. The invention is of particular advantage in providing a color passive film on zinc and cadmium in order to increase the corrosion resistance of articles made therefrom, or articles having a zinc or cadmium surface, such as zincor cadmium-based alloys, zinc castings, and, specifically, articles having a zincor cadmium-plated coating.

Zinc and cadmium become corroded in a relatively short time under the effect of atmospheric moisture. In order to extend the life of articles having a zinc or cadmium surface and to preserve their decorative appearance, they may be passivated in acid solutions of hexavalent chromium. Aqueous solutions are known in this art for passivating zinc and cadmium containing chromic anhydride, sulphate ions, boric and nitric acids (cf. US. Pat. No. 2,904,414), or hexavelent chromium, sulphate ions, nitrate ions and acetate or borate ions (cf. US. Pat. No. 3,121,032).

The use of a solution containing chromic anhydride, sulphate ions, boric and nitric acids involves intensive dissolving of the metal being passivated, particularly when an automatic passivating apparatus is employed. The preparation of the passivating solution and the process of passivating proper requires great amounts of concentrated nitric acid which presents difficulties in properly controlling the composition of the solution because of rapid accumulation of foreign matter therein. A zinc or cadmium surface passivated in such a solution does gain a decorative appearance, while its corrosion resistance increases only slightly.

The solution containing hexavalent chromium, sulphate ions, nitrate ions, and acetate or borate ions is conductive to the formation of colorless passive films on articles having a zinc or cadmium surface, but again their corrosion resistance fails to increase significantly.

The above methods can be applied in order to obtain decorative films on articles having a Zinc or cadmium surface. However, when tested in a fog of a neutral 5% aqueous solution of sodium chloride, a zinc or cadmium surface shows its first signs of corrosion even before a 20 to 30 hour period has expired.

It is an object of the present invention to provide a dry composition for preparing a solution for color passivation, in manual, or automatic apparatus.

Another object of the invention is to provide a dry composition for adjusting the solution for color passivation of zinc and cadmium.

Still another object of the invention is to provide a solution for color passivation of zinc and cadmium which does not require frequent replacement, but which is makes -t possible to replenish or make adjustment during the course of passivating.

Yet another object of the invention is to provide a method for obtaining color passive films on zinc and cadmium possessing high corrosion resistance.

These and other objects are achieved by applying a novel composition which is, according to the invention, a mixture of hexavalent chromium compounds, such as chromic anhydride and/or soluble chromates, and soluble nitrate compounds, soluble sulphate compounds,

soluble boron compounds and, an amino acid of the general formula:

COOH

hexavalent chromium compound (calculated as chromium) 1.7-70.0 nitrate compound (calculated as N0 1.0-45.0 sulphate compound (calculated as S0, 1.0-25.0 boron compound (calculated as boron) 0.5-10.0 amino acid 0.05-6.0

Hexavalent chromium compounds constitute the basic passivating agent. Its content in a composition for color passivation of zinc and cadmium should be 1.7 to 70.0 weight parts. Sulphate compounds are the main activators of the passivating process. Their concentration in a passivating composition, when calculated as $0 should vary from 1.0 to 25.0 weight parts. Nitrate compounds act as the oxidizing and brightening agents. Their concentration in the passivating composition, when calculated as N0 should be maintained within 1.0 to 45.0 weight parts. Boron compounds impart the polishing and brightening properties to the composition. Their concentration in a composition, when calculated as boron, should be from 0.5 to 10.0 weight parts. Amino acids are the stabilizing and buffering agents ensuring an extremely long life for the passivating composition. Their content in a composition should be from 0.05 to 6.0 weight parts.

It is expendient that apassivating composition contain (in weight parts):

hexavalent chromium compound (calculated as chromium) l 1.0-21 0 nitrate compound (calculated as N0 2.4-6.0 sulphate compound (calculated as $0. 2.2-7.0 boron compound (calculated as boron) 1.1 .3 amino acid 0.05-0.1

. paratus where substantial losses of the solution are sufhexavalent chromium compound (calculated as chromium) 11.0-21.0 nitrate compound (calculated as NO,,) 2.4-6.0 sulphate compound (calculated as S0, 2.2-7.0 boron compound (calculated as boron) 1.1-4.3 amino acid 0.5-4.0

It is advisable that the hexavalent chromium be introduced into the composition as chromic anhydride compounds; chromates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc; bi chromates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc; mixtures of said chromates; mixtures of said bichromates; mixtures of said chromates and with bichromates; mixtures of chromic anhydride and chromates; mixtures of chromic anhydride and bichromates; and mixtures of chromic anydride, chromates and bichromates, all being taken separately or in combinations.

It is most advisable that the nitrate beintrodu cgdinto the composition as nitrate compounds of ammonium, beryllium, potassium, sodium, cadmium, lithium, magnesium, zinc, all being taken separately or in combinations.

it is also advisable that the sulphate be introduced into the composition as sulphate compounds of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc, bisulphate compounds of ammonium, potassium, lithium, and sodium, all being taken separately or in combinations.

The boron should be preferably introduced into the composition as the following compounds: boric acid, magnesium orthoborate, and polyborates of ammonium, beryllium, potassium, lithium, magnesium, sodium, all being taken separately or in combinations.

It is most expedient that the amino acid have the general formula:

R1 R: n

where R, and R stand for l-l, Cl-1 -C 1-l s m maybe K=1-4; and n=1-5 The invention, according to one embodiment thereof, can provide a composition having the following content of its ingredients in an aqueous solution thereof (in g/l):

hexavalent chromium compound it is expedient that the content of the composition ingredients in an aqueous solution thereof be (in g/l):

hexavalent chromium compound solution pH 1.6-2.3

It is most expedient that the content of the composition ingredients in the aqueous solution thereof be (in 8/ hexavalent chromium compound (calculated as chromium) 1 10-210 nitrate compound (calculated as h1g6) 2.4-6.0 sulphate compound (calculated as 2.2-7.0 boron compound (caclulated as boron) 1.1-4.3 amino acid 0.5-4.0

The novel method for passivating zinc and cadmium by dipping them into an aqueous solution containing a hexavalent chromium compound comprises using a composition having the folowing ingredientcontents in an aqueous solution thereof (in g/l):

hexavalent chromium compound Lil-70.0 (calculated as chromium) nitrate compound (calculated as N0 Ill-45.0 sulphate compound (calculated as SO 1.0-25.0 boron compound (calculated as boron) (LS-10.0 amino acid ODS-6.0

the pH of the solution is from 1.1 to 2.8, and the zinc or cadmium is treated therein at a temperature of from 15 to 35C for a period of about 3 to seconds.

The proposed composition for color passivating zinc and cadmium is a mixture of non-volatile solid substances which is easy to prepare, to transport, to store and to use. The latter requirement is attained by an easy preparation of the passivating solution, as well as in the facile adjustment and control thereof. If neces sary, the composition may be prepared on the spot by conventional mechanical blending starting ingredients.

After the treatment by the proposed method, a bright color passive film is formed on the zinc or cadmium surface. This passive film has bright opalescent tints even if the zinc or cadmium surface was dull prior to treatment.

The passive films obtained by the novel method are abrasion-resistant in the course of passivating, therefore use may be made of manually operated and automatic apparatus of both stationary and rotary type may be used.

One of the chief advantages of the present invention is that the passive films obtained by the method provided herein have a high corrosion resistance. The passive film formed on a zinc or cadmium surface is tested for corrosion resistance by the so-called salt fog method whereby the film is subjected to a continuous action of a fog produced by spraying in a testing cabinet with a 5% aqueous neutral solution of sodium chloride at a temperature of 35 2*: 1C. The corrosion resistance of a film is determined by the time interval between the onset of the test and the moment of the ap- Example 1.

chromic anhydride (calculated as chromium) potassium chromate (calculated as chromium) cadmium nitrate (calculated as N0 potassium sulphate (calculated as 50 sodium tetraborate (calculated as boron) 0: -amino glutaric acid Example 2.

sodium bichromate (calculated as chromium) potassium nitrate (calculated as NO;,) 3 2 beryllium sulphate (calculated as $0 1.2 boric acid (calculated as boron) 2.7 0: -amino glutaric acid 0.0

Example 3.

chromic anhydride (calculated as chromium) ammonium nitrate (calculated as N0 lithium sulphate (calculated as SO magnesium orthoborate (calculated as boron) N(p-ethoxyphenyl 43 -aminopropionic acid Example 4.

beryllium bichromate (calculated as chromium) lithium chromate (calculated as chromium) zinc nitrate (calculated as N0 cadmium sulphate (calculated as SO ammonium pentaborate (calculated as boron) N-octylamino-acetic acid Example 5.

Example 6.

chromic anhydride (calculated as chromium) magnesium nitrate (calculated as N beryllium sulphate (calculated as S0, bonc acid (calculated as boron) 1.0 N-(B-hydroxyethyl)-iminodiacetic acid Illustrative examples of other amino acids used in the above compositions are:

Nitrilotriacetic acid lmino-diacetic acid N-phenyl-iminodiacetic acid Amino-acetic acid PPS.-

-Continued N N-dimethyl-aminoacetic acid N N-dieth l-amino-acetic acid N N-di(l} ydroxyethyl-amino-acetic acid N-(B-ammoethyl )-ammo-acetic acid a-aminopropionic acid N-(Bcyanoethyl)-a-aminopropionic acid a-(Bcyanoethyl l-aminoacetic acid N-(B-benzoylethyU-a-amino butyric acid fi-aminopro ionic acid B-amino iso utyric acid B-dimethyl-amino-fi-phenyllpmpionic acid B'dimethylaminobutyric aci N N-diw-carboethoxyethyl )-amino-acetic acid N-(n-dimethyl-aminophenyl)-a-aminopropionic acid 'y-aminobutyric acid e-aminocaproic acid 21 N-carboxymethyl-a-aminopropionic acid 22. a-(carboxymethyl-amino)-/3-aminopropionic acid 23. Arninosuccinic acid 24. a-aminobutyric acid 25. a-aminoisobumacid 26. a-amino-B-car 'do-propionic acid 27. a-aminoisovaleric acid 28. oz-aminocaproic acid 29. a-aminoisoca roic acid 30. a-amino B-p enyl-propionic acid.

A passivating solution is prepared by dissolving the dry passivating composition in water. In practical use, the solution is, if necessary, adjusted with an acid such I as sulphuric acid, or a hydroxide such as sodium hydroxide, to maintain the solution pH within a range of from 1.1 to 2.8. The preferable pH of the passivating solution within this range depends on the time of the treatment of a zinc or cadmium surface by the solution. In case the passivation takes little time (3 to 8 seconds), the optimum pH would be 1.1 to 1.7, and if passivating treatment lasts longer (20 to 16 seconds), the optimum pH would be from 1.7 to 2.5. For in order to obtain color passive films, on articles having a zinc or cadmium surface, said color passive films having a high corrosion resistance, as well as resistant to wet attrition, by using a passivating solution on a rotary apparatus, the optimum pH of the solution would be from 1.6 to 2.3.

When said solutions are used for color passivation of zinc and cadmium, their temperature should be maintained within a range of from 15 to 35C and, in order to obtain the best results, within a range of from 20 to 28C.

The time for treatment of a zinc or cadmium surface with a passivating solution may vary from 3 to sec, but usually it lies within 10 to 35 seconds. The higher the pH, the lower are the temperature and the concentration of the ingredients of the solution and the longer the time of passivation, and vice versa.

According to the present invention, articles having a zinc or cadmium surface are dipped into a passivating solution for a definite period of time depending on the properties of the solution, then removed therefrom, rinsed in running cold water, then in heated water, and, finally, dried. As a result of such treatment, the zinc or cadmium surface is coated with a color opalescent passive film of high corrosion resistance.

Given in Table l are the tolerable and optimum concentrations of ingredients of solutions for color passivation of zinc and cadmium according to the present invention.

7 Table 1 Permissible Optimum con- Optimum conlngredient concentraoentration centration h (s/ (al (al Hexavalent chromium compound (calculated as chromium) 1.7-70.0 11.0-21.0 11.0-21.0 Nitrate compound (calculated as NO,') l.0-4S.O 2.4-6.0 2.4-6.0 Slphatc compound culated as 50") 1.0-25.0 2.2-7.0 2.2-7.0 Boron compound (calculated as boron) 0.5-10.0 1.1-4.3 1.1-4.3 Amino acid ODS-6.0 ODS-0.1 0.54.0

In case a passivating solution is used on an apparatus noted for substantial losses thereof through being carried away by the workpiece surface, it is more preferable that the solution contain less amino acid.

In the course of passivation, the concentration of the solution ingredients is constantly diminishing due to a reaction between the workpiece surface and the solution, and a dilution of the solution. An outstanding feature of the present invention is the possibility of replenishing and adjusting the passivating solution, in the course of passivating the treatment, by adding the above dry passivating compositions and an acid in the amounts is dictated by the assays, e.g. hexavalent chromium and pH.

The novel method for color passivation of zinc and cadmium according to the invention is illustrated by Examples 7 and 8.

EXAMPLE 7.

208.74 g of the dry composition of Example 1 were dissolved in 3 of water. After adding 1.0 ml/l of H 80, (d 1.83) to a pH of 1.86, a passivating solution was obtained containing (in g/l):

hexavalent chromium N0 ion boron amino acid A steel workpiece was immersed into the prepared solution maintained at 23C was and, coated with bright zinc in a cyanide bath for zinc-plating, for a peface was coated with a bright color film with opalescent 5 5 tints.

Said solution was further used for passivating zinc articles. ln the'course of passivating, the solution was replenished with sulphuric acid and the dry passivating composition of Example 1 in amounts as based on the assays for pH and hexavalent chromium. Throughout the passivating process, the solution was adjusted by adding an amount of dry composition sufficient for the volume of the solution to become five-fold of that of which it originally was. After passivating zinc plated surfaces of 0.1, 1.0, 10.0 and 30.0 square meters the, samples were taken for corrosion tests in a salt-fog cabinet. The first signs of corrosion appeared, in the first three cases, after 120 hours and, in the fourth case, after hours of testing.

EXAMPLE 8.

750.0 g of the dry composition of Example 2 were dissolved in a 10 l-capacity bath on a rotary automatic apparatus noted for its marked dilution and for carrying away the passivating solution due to a large surface of the work being passivated. After adding 0.55 ml/l of sulphuric acid (d 1.83) to a pH of 2.16, a passivating solution was obtained containing (in g/l):

hexavalent chromium 18.3 0 ion 3.2 SO. ion 2.2 boron 2.7 amino acid 0.08

immersed into the prepared solution maintained at 25C for a period of 30 seconds was a drum loaded with steel workpieces coated with matte cadmium in a cyanide bath for cadmium-plating. At the expiration of this period, the drum was taken out, dipped into a bath with running cold water for a period of 30 seconds, then into a bath of heated (to 40C) water for a period of 30 seconds, and, finally, transferred to a desiccator where the cadmium-plated work-pieces were dried after passivation in hot (60C) air. As a result of this treatment, the cadmium-plated workpieces were coated with a bright color film with opalescent tints.

The passivation of the cadmium-plated workpieces continued in said apparatus. in the course of passivation, the solution was replenished with sulphuric acid and the dry passivating composition of Example 2 in amounts as based on the assay for pH and hexavalent v chromium. Throughout the passivating process, the solution was adjusted by adding an amount of dry composition sufficient to attain a twenty-fold increase of the initial solution volume. After passivating 0.4, 4.0, 40 and square meters of the cadmiumplated surface, the samples were taken for corrosion tests in a salt-fog cabinet. The first signs of corrosion appeared, in the first three cases, after 148 hours and, in the fourth case, after 120 hours of testing.

EXAMPLES 9 to 21.

Shown in table 2 various compositions of passivating solutions and the conditions for passivating zinc and cadmium therein.

Table 2 Example No. :9 :10 :11 :12 '13 .14 :15 :16 .17 18 :19 :20 :21

INGREDIENTS 8/ Cr (V1) 32.2 11.6 13.0 70.0 5.5 10.2 1.7 5.0 9.0 4.8 20.3 11.4 5.38 NO 18.6 2.3 1.0 20.1 5.0 1.0 4.3 3.6 1.0 1.3 1.0 4.81 10.6 $0, 4.3 3.6 4.6 25.0 2.7 2.8 1.0 4.4 5.2 1.2 1.07 7.08 6.8 B 2.2 0.94 10.0 0.5 0.5 1.9 3.0 0.5 1.08 0.5 0.57 1.13 2.98 amino acid 4.2 2.7 6.0 3.3 0.93 0.5 0.05 2.0 0.26 0.48 3.44 1.0 2.04 pH 1.35 2.06 2.8 1.1 1.25 1.62 2.45 1.35 1.8 1.33 1.89 1.52 1.6 tC 2O 27 15 22 27 20 35 22 20 25 20 30 t. sec 20 60 90 3 10 40 30 30 15 25 20 EXAMPLE 9. sodium chromate, magnesium nitrate, cadmium sul- A passivating solution was prepared by dissolving in water the respective amounts of chromic anhydride, sodium nitrate, zinc sulphate, lithium tetraborate, and N-(B-benzoylethyD-a-amino butyric acid.

EXAMPLE 10.

A passivating solution was prepared by dissolving in water the respective amounts of potassium chromate,

beryllium nitrate, zinc sulphate, boric acid, and a-amino-B(phenyl)-propionic acid.

EXAMPLE 14.

A passivating solution was prepared by dissolving in water the respective amounts of ammonium bichromate, potassium nitrate, potassium sulphate, lithium tetraborate, and a-amino-isocaproic acid.

EXAMPLE 15.

A passivating solution was prepared by dissolving in water the composition of Example 6.

EXAMPLE 16.

A passivating solution was prepared by dissolving in water the respective amounts of sodium chromate, sodium nitrate, sodium sulphate, potassium tetraborate, and ,B-aminopropionic acid.

EXAMPLE 17.

A passivating solution was prepared by dissolving in water the respective amounts of potassium bichromate, beryllium sulphate, zinc nitrate, potassium pentaborate, and a-amino-succinic acid.

EXAMPLE 18.

A passivating solution was prepared by dissolving in water the respective amounts of chromic anhydride,

phate, sodium tetraborate, and a(B'-cyanoethyl)- amino-acetic acid.

EXAMPLE 19.

A passivating solution was prepared by dissolving in water the respective amounts of chromic anhydride, potassium chromate, zinc nitrate, lithium sulphate, zinc borate, and a-aminoisovaleric acid.

1 EXAMPLE 20.

A passivating solution was prepared by dissolving in water the respective amounts of chromic anhydride, lithium sulphate, potassium nitrate, sodium tetraborate, and a-aminopropionic acid.

EXAMPLE 21.

A passivating solution was prepared by dissolving in water the respective amounts of chromic anhydride, sodium chromate, beryllium nitrate, potassium sulphate, lithium tetraborate, and N N-diethyl-aminoacetic acid.

In Examples 9, l2, 15, 19 and 20, the solution was adjusted in order to obtain the pH value given in Table 2 by adding therein sodium hydroxide, while in the other Examples, sulphuric acid was added for the same purpose.

Steel workpieces were passivated in Examples 10, ll 15, 18 and 20 having a bright zinc coating obtained in a cyanide bath, in Example 16, steel workpieces with a matte zinc coating obtained in a cyanide bath were passivated, and in Examples 9, l3 and 19, steel workpieces with a bright cadmium coating obtained in a cyanide bath, in Example 21, steel workpieces with a matte cadmium coating obtained in a cyanide bath, in Example l2, workpieces made of a zinc alloy, in Example 14, workpieces made of a zinc casting, and in Example 17, a steel workpiece coated with zinc by a hot process were also passivated.

In Examples l4, l5 and 20, passivation was effected by following the procedure of Example 8, and in' the other Examples, the workpieces were passivated by following the procedure of Example 7.

In each case, the treated workpieces were coated with a color opalescent film. The brightest films were obtained in Examples 9, l0, l3, l8 and 20.

The corrosion resistance of the passive films obtained by the novel method and which were tested in a salt fog cabinet is given in Table 3.

Table 3 Example No. 9 l2 13 14 What is claimed is:

l. A composition for the color passivation of zinc and cadmium consisting essentially of a mixture of hexava-- lent chromium compounds selected from the group consisting of chromic anhydride and soluble chromates, and soluble nitrate compounds, soluble sulphate compounds, soluble boron compounds, and an amino acid of the general formula:

COOH

where R R R R l-l, alkyl (C -C phenyl, substituted alkyls and phenyls, containing substituents OH, R, -COR, COOH, COOR, CONH 'CN,, -NH NHR, -RNR, (R alkyl, and aryl), n l 5, said composition having the following content of the above components (in weight parts):

hexavalent chromium compound (calculated as chromium 1.7-70.0 nitrate compound (calculated as N0 1.0-4S.0 sulphate compound (calculated as S0 l.0-25.0 boron compound (calculated as boron) 0.5-l0.0 amino acid 0.05-6.0.

2. A composition for color passivation of zinc and cadmium as claimed in claim 1, containing (in weight parts):

hexa alent chromium compound 1 (calculated as chromium) 11.0-21.0 nitrate compound (calculated as NO;,) 2.4-6.0 sulphate compound (calculated as S0,, 7) 2.2-7.0 boron compound (calculated as boron) 1.1-4.3 amino acid ODS-0.1.

3. A composition for color passivation of zinc and cadmium as claimed in claim 1, containing (in weight parts):

hexavalent chromium compound (calculated as chromium) 11.0-21.0 nitrate compound (calculated as N0 2.4-6.0 sulphate compound (calculated as SO 2.2-7.0 boron compound (calculated as boron) 1.1-4.3 amino acid 0.5-4.0.

and chromates, mixtures of chromic anhydride and bichromates, mixtures of chromic anhydride. chromates and bichromates,

5. A composition for color passivation of zinc and cadmium as claimed in claim 1, wherein the nitrate is introduced as compounds selected from the group consisting of nitrates of ammonium, beryllium, potassium, cadmium, lithium, mangesium, sodium, and zinc.

6. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the sulphate is introduced as compounds selected from the group consisting of sulphates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc, and bisulphates of ammonium potassium, lithium, and sodium.

7. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the boron is introduced as compounds selected from the group consisting of boric acid, magnesium orthoborate, and polyborates of ammonium, beryllium, potassium, lithium, magnesium, and sodium.

8. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the amino acid has the general formula:

hexavalent chromium compound (calculated as chromium 1.7-70.0 "see sweep-l su e com un cu a e as bor'on compo iid (calculated as boron) 0.5-l0.0 amino acid 005-61) and the solution pH 1.1-2.8.

10. A composition for the color passivation of zinc and cadmium as claimed in claim 9, wherein the content of its ingredients in the aqueous solution thereof being (in g/l):

hexavalent chromium compound (calculated as chromium? 11.0-21.0 nitrate compound Scalcu ated as N06) 2.4-6.0 sulphate compoun (calculated as S 2.2-7.0 boron compound (calculated as boron) 1.1-4.3 ammo aci 0.05-0.1

solution pH 1.6-2.3.

11. A composition for the color passivation of zinc and cadmium as claimed in claim 9, wherein the content of its ingredients in the aqueous solution thereof are (in g/l):

hexavalent chromium compound (calculated as chromium) l 1.0-2l.0 nitrate compound (calculated as N0 2.4-6.0 sulphate compound (calculated as S0 2.2-7.0 boron compound (calculated as boron) 1.1-4.0 amino acid 0.5-4.0

solution pH 1.6-2.3. 

1. A COMPOSITION FOR THE COLOR PASSIVATION OF ZINC AND CADMIUM CONSISTING ESSENTIALLY OF A MIXTURE OF HEXAVALENT CHROMIUM COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF CHROMIC ANHYDRIDE AND SOLUBLE CHROMATES, AND SOLUBLE NITRATE COMPOUNDS, SOLUBLE SULPHATE COMPOUNDS, SOLUBLE BORON COMPOUNDS, AND AN AMINO ACID OF THE GENERAL FORMULA:
 2. A composition for color passivation of zinc and cadmium as claimed in claim 1, containing (in weight parts):
 3. A composition for color passivation of zinc and cadmium as claimed in claim 1, containing (in weight parts):
 4. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the hexavalent chromium is introduced as compounds selected from the group consisting of chromic anhydride, chromates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc, bichromates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc, mixtures of said chromates, mixtures of said bichromates, mixtures of said chromates and bichromates, and mixtures of chromic anhydride and chromates, mixtures of chromic anhydride and bichromates, mixtures of chromic anhydride, chromates and bichromates,
 5. A composition for color passivation of zinc and cadmium as claimed in claim 1, wherein the nitrate is introduced as compounds selected from the group consisting of nitrates of ammonium, beryllium, potassium, cadmium, lithium, mangesium, sodium, and zinc.
 6. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the sulphate is introduced as compounds selected from the group consisting of sulphates of ammonium, beryllium, potassium, cadmium, lithium, magnesium, sodium, zinc, and bisulphates of ammonium potassium, lithium, and sodium.
 7. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the boron is introduced as compounds selected from the group consisting of boric acid, magnesium orthoborate, and polyborates of ammonium, beryllium, potassium, lithium, magnesium, and sodium.
 8. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the amino acid has the general formula:
 9. A composition for the color passivation of zinc and cadmium as claimed in claim 1, wherein the content of its ingredients in the aqueous solution thereof being (in g/l):
 10. A composition for the color passivation of zinc and cadmium as claimed in claim 9, wherein the content of its ingredients in the aqueous solution thereof being (in g/l):
 11. A composition for the color passivation of zinc and cadmium as claimed in claim 9, wherein the content of its ingredients in the aqueous solution thereof are (in g/l):
 12. A method for the color passivation of zinc and cadmium by comprising dipping them into an aqueous solution of the composition as claimed in claim 9 for a period of 3 to 90 seconds at a temperature of from 15* to 35*C. 